How Chain of Responsibility Pattern Powers PHP Middleware Stacks

The Soft PHP MVC framework implements the Chain of Responsibility design pattern to handle HTTP requests through a sequence of independent middleware layers. Each middleware unit receives an incoming request and either processes it, modifies it, or passes it to the next handler in the chain. Security-focused middleware like CsrfMiddleware and RateLimitMiddleware can short-circuit the chain by returning error responses before a request reaches the application controller. New middleware such as VisitorTrackingMiddleware can be added without modifying any existing components, demonstrating the Open/Closed Principle in practice. This pattern has become a de facto standard in modern PHP frameworks including Laravel, Symfony, and Slim.